This invention relates to gas turbine engines and, more particularly, to thrust vectorable nozzles for use therein.
The thrust produced by a gas turbine engine is substantially parallel with and opposite to the direction of the exhaust gases flowing therethrough. Therefore, if the direction of the exhaust gases exiting an engine is changed, the direction of the resulting thrust is correspondingly varied. Advanced aircraft configurations contemplate the selective redirection (or vectoring) of gas turbine engine thrust in order to improve aircraft performance and to provide the aircraft with operational characteristics heretofore deemed impractical. For example: if the exhaust of a conventionally installed gas tubine engine was directed downward, rather than rearward, to a direction substantially perpendicular to the engine longitudinal axis, the upward thrust would provide direct lift, and therefore, a vertical take-off and landing capability. Similarly, thrust vectoring in flight can greatly increase aircraft maneuverability since the thrust force can augment maneuvering forces heretofore created solely by aircraft control surfaces such as elevators, ailerons and rudders. In order to accomplish such thrust vectoring, a device is required to efficiently and practically alter the direction of gas turbine engine exhaust nozzle gases.
Target-type diverters have been utilized to divert the exhaust gases after they exit from the nozzle, but these claim shell-like devices are large and heavy and not readily adaptable to the intricate thrust vectoring contemplated for advanced engine applications. Therefore, efforts have been concentrated on diverting the exhaust gases through one of several exhaust ports of a gas turbine exhaust nozzle, one of which is normally of the swivelable, thrust vectoring type. The diversion is accomplished by selective positioning of a diverter valve (such as a swivelable door) within the exhaust nozzle. However, the effective sealing of irregular or non-precision, valve-type joints under the elevated temperature experienced in gas turbine exhaust nozzles has long been a severe problem.
In exhaust nozzle applications, the operating temperatures are too high to permit the use of available elastomer materials which could otherwise be used to assure effective sealing between the diverter valve and the nozzle exhaust port. Metallic materials are able to tolerate the temperatures involved and these, due to their relative inelasticity, are not easily conformable to the structures to be sealed. Even when manufactured as segmented seals for improved conformance, intersegment leakage can be as high as 1% of total engine airflow, resulting in a reduction of overall engine performance.
The sealing problem in lightweight, high temperature diverter valves is further complicated by the fact that lightweight sheet metal construction is inherently not conductive to an accurately fitting valve. Additionally, thermal expansion and thermal cycling accentuate the valve fit problem. And, finally, the often complex shape of the exhaust port to be sealed and the characteristic pivoting motion of the clam shell-type diverter valve segments have generally precluded the use of continuous seals.
The problem facing the mechanical designer, therefore, is to provide an effective lightweight sealing means for a high temperature, irregularly shaped, sheet metal gas turbine exhaust nozzle. Prior state-of-the-art attempts to solve this problem have been oriented toward providing a segmented bumper seal about the exhaust port upon which the diverter valve slidingly abuts. Since it is extremely difficult to construct a continuous bumper seal about an essentially circular exhaust port and still permit the diverter valve to slidingly rotate to another deployed position, and since substantial radial gaps are required between the diverter valve and the exhaust port to account for thermal growth and permit free rotation of the diverter valve, significant leakage remains in such a system.